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22. Appendix 4: pH Electrode Care
Electrode Calibration
Since glass pH electrodes measure H+ concentration relative to their reference half-cells, they must be
calibrated periodically to ensure accurate, repeatable measurements. Our wide selection of commercial
pH calibration buffers include solutions standardized against NIST-certified pH references for calibrating
meters with resolution up to 0.001 pH.
Although calibration against one pH reference buffer (one-point calibration) typically ensures accurate pH
measurement, frequent two-point or even three-point calibrations ensure the most reliable results. Make
sure your pH system includes calibration buffers for a range of pH values.
Conditioning
pH electrodes are shipped with the electrodes moist. Prior to using your electrode for the first time,
follow these three steps to condition your electrode:
1. Remove the protective cap or rubber boot from the bottom of the sensor and rinse the electrode
with distilled or deionized water.
2. Place the electrode in a beaker containing one of the liquids listed below (in order of ionic ability
to condition the electrode). Soak for 20 minutes.
• 3.8 M or 4.0 M KCL
• 4.0 pH buffer
• 7.0 pH buffer
NOTE: Never condition a pH electrode in distilled or deionized water. Long term exposure to pure
water will damage the special glass membrane.
3. After conditioning the sensor for 20 minutes, rinse the electrode with distilled or deionized water.
The electrode is now ready for calibration and to measure pH.
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